1. Field of the Invention
The present invention relates to a reception apparatus, and more particularly, to a reception apparatus using a spread spectrum communication scheme.
2. Description of the Background Art
Recently, in the field of mobile communication and the like, a spread spectrum communication scheme is receiving attention. Generally, a demodulation unit of a conventional reception apparatus using the spread spectrum communication scheme is roughly divided into three blocks of a searcher unit, a spread spectrum demodulation unit, and a decode unit. The searcher unit searches the channel and the path of a reception signal. The spread spectrum demodulation unit despreads the spectrum of the reception signal and performs phase correction and rake combination of the reception signal. The decode unit performs viterbi error correction and the like of the reception signal subjected to the rake combination.
The conventional spread spectrum demodulation unit receives a despread timing signal from the searcher unit, and demodulates the reception signal according to this despread timing signal. The conventional searcher unit generally uses, as acquisition means, a matched filter. Since the conventional matched filter receives data being passed as it is, it is capable of performing an acquisition at that time point, but not capable of detecting an acquisition point before and after that time point. Additionally, the conventional spread spectrum demodulation unit has many operation demodulation units that correspond to respective paths and that is referred to as fingers so as to improve accuracy of rake combination.
A conventional reception apparatus disclosed in Japanese Patent Laying-Open No. 10-209919, when combining a demodulation output of each path by a data combiner, stores the demodulation output of each finger in a memory with a value of PN (Pseudorandom Noise) phase counter indicative of the phase of PN code of each finger set as a write address, and reads data of each memory with a common read address.
A conventional matched filter and CDMA (Code Division Multiple Access) reception apparatus disclosed in Japanese Patent Laying-Open No. 2000-307471 obtains correlation values generated among a plurality of signals arrived through multipath and chip delay information of the plurality of signals behind a reference reception timing signal surely and easily without increasing the circuit scale, and performs a rake combination process, monitoring of a delay profile and other operations.
The conventional reception apparatuses each demodulate a reception signal according to a despread timing signal from the searcher unit. Accordingly, there has been a problem that the searcher unit that occupies a circuit area is essential. Further, the matched filter used in the conventional searcher unit is not capable of detecting an acquisition point before and after the time point at which data is passed. Therefore, acquisition has been required to be repeated every time an instantaneous interrupt of synchronization occurs, and therefore time has been required. Still further, as the conventional reception apparatuses each require many finger operation units, there has been a problem that the circuit scale is increased.
Though the conventional reception apparatuses disclosed in the aforementioned patent documents may be certain means for solving part of the aforementioned problems, means for solving such problems are not limited to the means disclosed in the patent documents.